透過表面改質工程提高二維錫鹵化物鈣鈦礦電晶體的性能和穩定性及其對光記憶行為的影響

Abstract

近十年來，金屬鹵化物鈣鈦礦因其具高吸收係數、低激子結合能和長載流子壽命，在半導體領域引起了極大的關注。這些特性使其適用於電子元件發展，如鈣鈦礦太陽能電池(PVSC)、鈣鈦礦發光二極體(PeLED)、鈣鈦礦場效應電晶體(PeFET)等。然而，鉛基鈣鈦礦總是被批評具高環境毒性，同時，由於鉛具有相對高的有效載子質量，導致鉛基鈣鈦礦電晶體的載子遷移率普遍偏低。因此，有越來越多的研究將鉛替換成錫，並致力於開發二維錫基鹵化物鈣鈦礦電晶體，其中最著名的體系為苯乙基錫碘化铵 (PEA2SnI4)，其具有適當的能隙並在室溫下可展現較高的載子遷移率。然而，錫基鹵化物鈣鈦礦具有較快的結晶速率，造成其製備薄膜質量較低，同時，Sn2+在含氧環境中容易氧化成Sn4+，限制了其廣泛應用性。在此，我們採用了界面工程改善二維錫基鈣鈦礦的膜況，減少缺陷並提高空氣穩定性，最終也證明這些改質可以同時提高電晶體元件的性能與穩定性。 在第二章中，我們使用了PEAI/FPEAI對PEA2SnI4薄膜進行表面鈍化處理，大大的提高了鈣鈦礦場效電晶體的性能和穩定性。鈍化過程中引起的表面再結晶增加了晶粒尺寸減少表面缺陷，同時，PEA+和FPEA+陽離子團上的氮原子可與Sn2+形成路易斯酸鹼對有效減少Sn空缺數量，進而改善膜況。此外，表面鈍化可以p型摻雜PEA2SnI4薄膜，促進鈣鈦礦與電極之間更好的能級匹配，實現高效的電荷傳輸。PEAI和FPEAI表面鈍化的元件測得的最大載子遷移率(μh)有明顯的增加，分別為2.15和2.96 cm2 V−1 s−1，遠高於對照組的μh (0.76 cm2 V−1 s−1)。此外，這些疏水的鈍化劑還能夠起到保護PEA2SnI4薄膜的作用，減緩空氣水氧引起的降解，這一個論點乃是透過XPS、UV和XRD等分析來證明。此外，鈣鈦礦薄膜中缺陷的減少間接提高了元件的閘極偏壓穩定性。最後，我們證明了鈣鈦礦場應效電晶體的非揮發性光記憶行為，並利用它們來製作鈣鈦礦場效應電晶體式的記憶體。總結來說，PEAI/FPEAI的表面鈍化不僅降低了鈣鈦礦薄膜的表面缺陷數量、提高環境穩定性，同時還增強了元件的光響應電流。我們的研究成果凸顯了表面鈍化在提高鈣鈦礦場效電晶體的性能和穩定性方面的幫助，這對於先進光電元件的發展有重要的影響。 在第三章中，我們通過旋塗法製備了TEA2SnI4的二維錫鹵化物鈣鈦礦薄膜。我們首先比較了PEA2SnI4和TEA2SnI4的光學性質、膜況和能階。接下來，我們將TEA2SnI4應用於場效應電晶體元件並發現其最大載子遷移率可達2.48 cm2 V-1 s-1，高於先前的PEA2SnI4體系，同時也是目前所有TEA2SnI4相關論文中最高的報導值。此結果可能來自於TEA2SnI4與金電極有更好能級匹配或是TEA+陽離子團較高之介電常數。我們目前正針對這個具有更高載子遷移率的二維錫基鹵化物鈣鈦礦體系進行添加劑與表面改質工程等，以期在未來達到更理想的性能。

Organic-inorganic metal halide perovskites have attracted a great deal of interest in the semiconductor field in the last decade due to their high absorption coefficients, low exciton binding energy, and long carrier lifetime. These properties make them suitable for electronic applications such as perovskite solar cells (PVSC), perovskite light emitting diodes (PeLED), perovskite field effect transistors (PeFET), etc. Among these, two-dimensional organic-inorganic metal halide perovskites are potential candidates for transistor applications because of their quantum effects and high structural stability. However, lead-based perovskites have long been criticized for their high toxicity to the environment. Meanwhile, the effective mass of the carriers is relatively large and their carrier mobility in transistors is low. Therefore, many studies have replaced lead with tin and worked on two-dimensional (2D) tin halide perovskites-based transistors, such as phenethylammonium iodide (PEA2SnI4). They have a suitable band gap and high mobility. However, excessively fast crystallization rate for tin-based perovskites contributes to low quality morphology. Also, the easy oxidation from Sn2+ to Sn4+ in the environment limits their wide applicability. Herein, we used an interfacial engineering approach to improve morphology, reduce defect density, and improve the air stability of 2D tin perovskites. The results further demonstrate that this modification method improves the performance of 2D tin perovskite transistors and enhances their air stability at the same time. In Chapter 2, we have shown that surface passivation of PEA2SnI4 films with PEAI/FPEAI significantly improves the performance and stability of the derived perovskite transistors. Surface recrystallization induced by surface passivation further reduces surface defects and increases grain size. The electron-donating pairs of nitrogen atoms on PEA+ and FPEA+ form Lewis acid-base pairs with Sn2+ and reduce Sn vacancies, resulting in improve films. Additionally, these passivators are able to p-dope the PEA2SnI4 films, promoting better energy-level alignment with the electrodes and enabling efficient charge transfer. The PEAI- and FPEAI-passivated devices showed a significant increase in maximum hole mobility (μh) of 2.15 and 2.96 cm2 V−1 s−1, respectively, exceeding the value (0.76 cm2 V−1 s−1) of the control device. These hydrophobic passivators also provided protection against ambient air-induced degradation of PEA2SnI4 film, as evidenced by XPS, UV, and XRD analyses. Moreover, they enhanced the gate bias stability of the devices by reducing defects in the perovskite films. Ultimately, we demonstrate the non-volatile photomemory behavior of perovskite transistors and leverage them for perovskite-transistor-based memories. In conclusion, surface passivation with PEAI/FPEAI not only reduces surface defects and improves the air stability of perovskite films, but also improves the photoresponse of the devices. Overall, this work highlights the importance of surface passivation in enhancing the performance and stability of perovskite transistors, which is of great importance for the development of advanced optoelectronic devices. In Chapter 3, we fabricated 2D tin halide perovskite films of TEA2SnI4 by spin-coating. And we first compared the optical properties, morphology, and energy level of PEA2SnI4 and TEA2SnI4. Next, we applied TEA2SnI4 to transistor devices with a maximum hole mobility of 2.48 cm2 V-1 s-1. This mobility is not only higher than that of PEA2SnI4 in our experiment, but also is the highest of all TEA2SnI4-related studies reported to date. This result could result from a better energy alignment or a higher dielectric constant of the TEA+ spacers. My group are currently working on additive and surface modification engineering for this 2D tin system with higher carrier mobility to achieve better performance in the future.